Since the discovery that certain ceramic materials could be superconducting at temperatures significantly higher than that of liquid helium, the research community has embarked on a wide ranging search for other ceramics having higher critical temperatures (Tc). As of this writing, researchers have found that certain ceramic compositions become superconductive at temperatures in excess of the temperature of liquid nitrogen (77.degree. K.). Almost on a weekly basis, papers are being published disclosing new ceramic materials and compositions which exhibit superconducting properties in the liquid nitrogen regime.
One problem which has received little public notice to date, is that it is difficult to characterize the superconducting properties of these new high Tc materials. On presently used test method involves making electrical contact to a sample and taking measurements of electrical resistance. An obstacle to the application of that method is the high contact resistance that often occurs where the contacts attach to the sample. Efforts have been made to overcome this problem but the preparation of the contacts and the subsequent testing of the superconductor, together, are quite complex. (e.g. see "Method for Making Low-Resistivity Contacts to High Tc Superconductors" by Ekin et al, Applied Physics Letters, Volume 52, Number 4, 25 Jan., 1988).
Others have attempted to determine the qualitative superconducting properties of a material by attempting to float a magnet above the sample. It is known, that when a magnet is bought into proximity with a superconducting sample, its magnetic field induces "super-currents" within the sample. The super-currents then generate their own magnetic field which is repulsive to the field created by the magnet. With the discovery of high Tc superconductors, it has been repeatedly shown that a small magnet can be stably levitated over a superconducting disk. What was surprising from those demonstrations was the finding that a small magnet would float above a superconducting disk at an equilibrium position over the disk's center, stable against lateral displacements. This phenomenon, while interesting, does not provide a quantitative characterization of the material other than simply to say that it is superconducting. There is no indication in such a test as to whether the material exhibits either homogeneous or heterogeneous superconducting properties.
Accordingly, it is an object of this invention to provide a system for determining superconductive properties of a sample which is both simple to operate and sophisticated in its measurement technique.
It is another object of this invention to provide a system for determining superconductive properties of a sample which avoids the necessity for making any connections to the sample.
It is a further object of this invention to provide a system which provides quantitative determinations of the magnetic superconducting properties of a sample.
It is still another object to this invention to provide a system for determining superconductive magnetic properties of a sample which is adapted to determine the homogeneity of the sample's superconducting properties.